First, I'll point you towards the Thunderbolt Display manual.
Second, with a stand-mounted display, basic reasoning indicates that the distance between the display's "bottom edge" and the surface of a desk is equal to the gap between the "bottom edge" and the part of the stand that rests on a desk.
Are you asking because you plan to mount the display somehow; mount it in a confined area?
If not, this question is revealing.
Thanks for your response.
Let me clarify --- yes, I am looking to mount it somehow in a relatively confined area. And I would like the profile to be as low as possible, so I can look over the edge of the screen. Ideally, I would lower it all the way down onto the desk. But that would inhibit the ability for cool air to be pulled in - which I believe happens through the bottom.
As I detailed in my reply to your other post, I have mine pretty much all the way to the desk and haven't had any problems. The display doesn't have a fan so it isn't active intake of air from the bottom. There isn't a top vent so it is just for some heat/air to passively escape. The speakers are also down there but with the 1/4" space I have is plenty for the general sound to get out and the air to get in. If I want it to sound a bit better, I just lift it up about an inch.
Having it up an inch from the desk may not be required, but it sure does help the sound. I now have my screen mounted hovering an inch above the desk surface and have found that not only does it help the sound but it also allows for me to move the keyboard and mouse to slide under it if I want the desk space AND it helps in some cases to have the space to let a cable through.